Aluminum, symbol Al, the most abundant metallic element in the earth\'s crust. The atomic number of aluminum is 13; the element is in group 13 (IIIa) of the periodic table.
Hans Christian Orstead, Danish chemist, first isolated aluminum in 1825, using a chemical process involving potassium amalgam. Between 1827 and 1845, Friedrich Wöhler, a German chemist, improved Oersted\'s process by using metallic potassium. He was the first to measure the specific gravity of aluminum and show its lightness. In 1854 Henri Sainte-Claire Deville, in France, obtained the metal by reducing aluminum chloride with sodium. Aided by the financial backing of Napoleon III, Deville established a large-scale experimental plant and displayed pure aluminum at the Paris Exposition of 1855.
Aluminum is a lightweight, silvery metal. The atomic weight of aluminum is 26.9815; the element melts at 660° C (1220° F), boils at 2467° C (4473° F), and has a specific gravity of 2.7. Aluminum is a strongly electropositive metal and extremely reactive. In contact with air, aluminum rapidly becomes covered with a tough, transparent layer of aluminum oxide that resists further corrosive action. For this reason, materials made of aluminum do not tarnish or rust. The metal reduces many other metallic compounds to their base metals. For example, when thermite (a mixture of powdered iron oxide and aluminum) is heated, the aluminum rapidly removes the oxygen from the iron; the heat of the reaction is sufficient to melt the iron. This phenomenon is used in the thermite process for welding iron .
The oxide of aluminum is amphoteric—showing both acidic and basic properties. The most important compounds include the oxide, hydroxide, sulfate, and mixed sulfate compounds. Anhydrous aluminum chloride is important in the oil and synthetic-chemical industries. Many gemstones—ruby and sapphire, for example—consist mainly of crystalline aluminum oxide.
Aluminum is the most abundant metallic constituent in the crust of the earth; only the nonmetals oxygen and silicon are more abundant. Aluminum is never found as a free metal; commonly as aluminum silicate or as a silicate of aluminum mixed with other metals such as sodium, potassium, iron, calcium, and magnesium. These silicates are not useful ores, for it is chemically difficult, and therefore an expensive process, to extract aluminum from them. bauxite an impure hydrated aluminum oxide, is the commercial source of aluminum and its compounds.
In 1886 Charles Martin Hall in the United States and Paul L. T. Héroult in...